1. Field of the Disclosure
The present invention generally relates to light diffusers for illuminating environments or objects and methods of manufacturing light diffusers.
2. Background Information
Light sources used for illumination typically require diffusers to diffuse or to spread out or to scatter the light to produce soft light, which generally cast shadows with no edges or soft edges as opposed to sharp edges. For example, in photography, soft light is used to reduce visibility of wrinkles for people to achieve a more youthful look.
Typical diffusers are hazy in appearance, or the diffusers are opaque or non-transparent. That is, an observer cannot see objects clearly through a typical diffuser. Typical diffusers may include for example, ground glass diffusers, teflon diffusers, holographic diffusers, opal glass diffusers, and greyed glass diffusers. Because such diffusers are not transparent, their presence in the view of observers may seem distracting and unpleasant. Additionally, typical diffusers may scatter significant amount of light back toward the light source, and thus, efficiency of the light source is reduced when such typical diffusers are used.
FIG. 1 illustrates a conventional diffuser panel, which may be for example, a ground glass diffuser panel.
Such conventional ground glass diffuser panels are isotropically diffusive and therefore look hazy and not transparent. As illustrated in FIG. 1, when light, generally with wavelength in the visible band, intersects the diffusive surface 12 of the diffuser panel 10, the uneven and rough texture of the diffusive surface causes the light to become scattered or diffused in nearly all directions, depending on the varying surface angles of the diffusive surface. The diffuser panel 10 comprises another surface 14, which may be generally flat or can be another diffusive surface. Because the light is diffused in nearly all directions, the diffuser is called isotropically diffusive. Furthermore, because the diffuser is isotropically diffusive, regardless of the angle of the incident light intersecting the diffusive surface, normal incident light, which is light intersecting generally perpendicularly to the plane of diffuser (θin=0), would also be diffused isotropically. This would thus cause objects to appear hazy and not clearly visible when viewed through such conventional ground glass diffusers, thus making the conventional ground glass diffusers appear opaque or non-transparent.
FIG. 2 illustrates another conventional diffuser panel, which may be for example, an ordinary grating type diffuser panel with a grating period (not shown) greater than the wavelengths of visible light.
Such conventional ordinary grating diffuser panels are also isotropically diffusive and therefore look hazy and not transparent. As illustrated in FIG. 2, light intersects the diffusive surface 22 of the diffuser panel 20. The diffusive surface 22 has a grating period (not shown). The grating period is the distance between the corresponding edges of adjacent grooves of the grating. The grating period (not shown) of such a conventional ordinary grating diffuser panel is greater than the wavelengths of visible light. The grating of the diffusive surface 22 causes the light to become scattered or diffused in nearly all directions. The diffuser is therefore also isotropically diffusive. This causes the grating surface to appear non-transparent. The diffuser panel 20 has another surface 24, which may be generally flat. Furthermore, because the diffuser is generally isotropically diffusive regardless of the angle of the incident light intersecting the diffusive surface, normal incident light (θin=0) would also be diffused isotropically. This would thus cause objects to appear hazy and not clearly visible when viewed through such conventional ordinary grating diffusers, thus making the conventional ordinary grating diffusers appear opaque or non-transparent.
FIG. 3 illustrates a conventional subwavelength anti-reflective (AR) surface panel with a binary grating, which looks transparent but does not defuse light.
As illustrated in FIG. 3, the conventional subwavelength binary grating panel 30 has a surface 32 with grating period P1 and another surface 34 which may be generally flat.
The grating equation showing the relationship between the grating period p, refractive index of incident side nin, refractive index of exit side nd incident angle θin, diffraction angle θd, incident light wavelength λ, and diffraction order m (integer) is given by,p(nd sin θd−nin sin θin)=mλ  (1)
The conventional subwavelength AR binary grating surfaces may satisfy,
where the grating period p=P1, and P1<λ/(nd+nin) (2)
When equation (2) is true, then there is no solution for equation (1) for diffraction orders (where |m| is greater or equal to 1, and |sin θin|≦1), and only zero order diffraction occurs for all incident angles.
For example, if nd=1 (air), nin=1.5 (acrylic), then if the grating period P1<λ/2.5, the panel will not diffract light of λ. If λ=0.39 um (the low wavelength end of the visible spectrum), then if P1<0.156 um, P1 would be less than λ/2.5 for all the higher wavelengths of the visible spectrum as well, and the panel will not diffract any visible light.
In such a case, there is no diffraction of light, such that the light can transmit through the panel without being diffracted. This would cause objects to be clearly visible when viewed through such conventional subwavelength binary grating from any angle, thus making the conventional subwavelength binary grating appear transparent. Because there is also little to no reflection of light in the conventional subwavelength binary grating, the conventional subwavelength binary grating would also appear to be anti-reflective.
Therefore, a transparent diffuser that can provide higher efficiency of lighting and a more pleasant transparent view may be needed.